KR20140016334A - Powder-classification method - Google Patents

Abstract

In the method of classifying powder, a mixing step of mixing the powder and the liquid preparation, a drying step of drying the powder mixed in the mixing step, an input step of introducing the powder dried in the drying step into a fluid classifier; And a heating step of heating the gas, a supply step of supplying the gas heated in the heating step to the fluid classifier, and a classification step of classifying the powder in the fluid classifier according to the particle size.

Description

Classification method of powder {POWDER-CLASSIFICATION METHOD}

The present invention relates to a method for classifying powders that effectively classifies powders having a particle size distribution at a desired classification point (particle size).

When classifying powder, such as glass blast furnace slag, into fine powder and coarse powder, the classification method which adds preparation of fluids, such as alcohol, is known (for example, refer patent document 1). In this classification method, a preparation containing polar molecules is added to the powder to electrically neutralize the polarity of the powder particles, thereby preventing the particles from adsorbing and agglomerating to form agglomerated particles having a large particle size, thereby lowering the classification efficiency. Is preventing.

Japanese Patent Publication No. 64-85149

By the way, today, for example, a ceramic used as a dielectric of a ceramic multilayer capacitor is manufactured by sintering fine powder of barium titanate (BaTiO ₃ ) having a very small average particle diameter of 0.7 µm. In order to obtain a high quality ceramic, not only the average particle diameter is very small, but the width | variety of the particle size distribution is very narrow, ie, a more homogeneous fine powder is required. Such fine powder can be obtained by classifying powder as a raw material, for example, by centrifugal separation, but in the conventional classification method, the powder of the raw material adheres to each part in the classifier, and the inlet of the raw material or the outlet of the high pressure gas is blocked. Therefore, deterioration of classification performance has been caused, making driving difficult for a long time.

The subject of this invention is providing the classification method of the powder which can classify efficiently, without attaching powder to a classifier even when classifying the powder whose particle diameter is less than 1 micrometer.

The classification method of powder of this invention WHEREIN: In the classification method of powder, the mixing process which mixes powder and a liquid preparation, the drying process which dries the said powder mixed by the said mixing process, and the said powder dried at the said drying process Is supplied to the fluid classifier, a heating step of heating the gas, a supply step of supplying the gas heated in the heating step to the fluid classifier, and classifying the powder in the fluid classifier according to the particle size. It is characterized by including a classification process.

Moreover, the classification method of the powder of this invention WHEREIN: In the classification method of powder, the mixing process which mixes powder and a liquid preparation, the drying process which dries the said powder mixed in the said mixing process, and the drying process dried And a feeding step of injecting the powder into the fluid classifier, a supply step of supplying gas to the fluid classifier, and a classification step of classifying the powder in the fluid classifier according to the particle size.

Moreover, the classification method of the powder of this invention is characterized by the drying temperature and drying time in the said drying process being a drying temperature according to the flash point of the said liquid preparation, and drying time.

Moreover, the classification method of the powder of this invention is characterized by heating the said gas so that the temperature in the said fluid classifier may be more than the flash point of the said liquid preparation and 200 degrees C or less in the said heating process.

Moreover, the classification method of the powder of this invention is characterized by the said gas supplied by the said supply process being a high pressure gas.

Moreover, the classification method of the powder of this invention is characterized by classifying the said powder by the swirling airflow which generate | occur | produced in the said fluid classifier in the said classification process.

Moreover, the classification method of the powder of this invention is characterized in that the said liquid preparation is diethylene glycol monomethyl ether.

Moreover, the classification method of the powder of this invention is characterized in that the said powder is powder of barium titanate.

According to the powder classification method of the present invention, even when the powder having a particle size of less than 1 µm is classified, the powder can be efficiently classified without attaching the powder to the fluid classifier.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram which shows the structure of the classification apparatus which concerns on 1st Embodiment.
It is a longitudinal cross-sectional view which shows the structure of the inside of the classifier which concerns on 1st Embodiment.
3 is a cross-sectional view showing the configuration of the interior of the classifier according to the first embodiment.
4 is a flowchart for explaining a method for classifying powder according to the first embodiment.
5 is a flowchart for explaining a method for classifying powder according to the second embodiment.

Hereinafter, a method of classifying a powder according to the first embodiment of the present invention will be described with reference to the drawings. FIG. 1: is a schematic block diagram which shows the structure of the classification apparatus which is a fluid classifier used by the classification method of powder which concerns on this embodiment.

As shown in FIG. 1, the classifier 2 inputs powder into the classifier (fluid classifier) 4 and the classifier 4 which classify the powder thrown in as a raw material by the swirling airflow generated inside. A feeder (6), a compressor (8) for supplying high pressure gas to the classifier (4), and a first heater (10) for heating the supplied high pressure gas to a predetermined temperature; have. In addition, the classifier 2 is a negative pressure generated in the suction blower 12 and the classifier 4 which suck and collect the fine powder separated to the desired classification point or less together with the gas in the classifier 4. 2nd heater 14 which heats the atmosphere (atmospheric gas) suctioned by (iii), and the collection | recovery container 16 which collects the coarse powder with a large centrifuged particle diameter.

The classifier 4 which has a substantially conical shape is provided so that the vertex of a cone may face downward, and the centrifuge chamber 20 (refer FIG. 2) mentioned later in detail above the classifier 4 is provided. Formed. Into this centrifugal chamber 20, atmospheric air as an atmospheric pressure gas existing outside the classifier 4 and a high pressure gas from the compressor 8 are supplied, and powder as a classification target is fed from the feeder 6. do.

The feeder 6 has a screw which is not shown in the inside, and by rotating the screw, the feeder 6 can quantitatively deliver the powder contained therein. The powder sent out is introduced into the classifier 4 from the inlet port 26 (see FIG. 2) provided on the upper surface of the classifier 4. On the other hand, the powder accommodated in the feeder 6 is previously mixed with the liquid preparation mentioned later in detail.

The compressor 8 compresses the atmosphere to generate a high pressure gas, and supplies it into the classifier 4 through the first heater 10. The 1st heater 10 has piping in which a high pressure gas passes, and the heating means which consists of a filament, an aerofin, etc. is provided in the piping. This heating means heats the high pressure gas which passes through the said piping to predetermined temperature. On the other hand, between the compressor 8 and the classifier 4, another dewatering means for removing the water containing the high pressure gas may be separately provided, or a filter for removing dust or the like may be appropriately provided.

The suction blower 12 is used to separate the fine powder separated by the classifier 4 from the suction port 32 (see FIG. 2) provided in the center of the upper surface of the classifier 4 in the classifier 4. Recover by inhalation together. On the other hand, a filter such as a bug filter may be appropriately provided between the suction port 32 and the suction blower 12. Here, when the gas is sucked by the suction blower 12, since negative pressure is generated in the classifier 4, the atmosphere, which is the atmospheric pressure gas existing outside the classifier 4, is sucked into the classifier 4. . In this way, when atmospheric pressure gas is sucked in, in the centrifugal separation chamber 20 of the classifier 4, the swirling airflow which rotates at high speed is formed. On the other hand, since the classification apparatus 2 which concerns on this embodiment is equipped with the 2nd heater 14 which heats the normal-pressure gas suctioned, it heats the temperature of the turning airflow in the centrifugation chamber 20 to predetermined temperature. can do. Similar to the first heater 10, the second heater 14 has a pipe through which the atmospheric gas passes, and heating means such as filament and aerofin are provided in the pipe.

The recovery container 16 is provided in the lowest part of the classifier 4, and collect | recovers the coarse powder dropped along the inclined surface of the cone-shaped part of the classifier 4, after being centrifuged in the centrifuge chamber 20. As shown in FIG.

Next, the classifier 4 which concerns on this embodiment is demonstrated with reference to FIG. 2 and FIG. 2 is a longitudinal cross-sectional view by the surface containing the central axis of the classifier 4, and FIG. 3 is a cross-sectional view at the position of the centrifugal separation chamber 20 by the plane perpendicular | vertical to the said central axis. On the other hand, in order to clarify the relative positional relationship with other components (in particular, the jet nozzle 30 and the guide vane 40, which will be described later), the inlet 26 and the jet nozzle (originally not shown in Fig. 3) 30 is shown by an imaginary line and a dotted line, respectively. In addition, only two jet nozzles 30 are shown for description.

As shown in FIG. 2, in the upper part of the classifier 4, the upper disk-shaped member 22 which has a flat disk shape, and the lower disk-shaped member 24 which has a disk shape with a hollow inside are provided a predetermined space | interval. It is hold | maintained and arrange | positioned, The cylindrical centrifugal chamber 20 is formed between both disk-shaped members. Above the centrifugal chamber 20, an injection port 26 through which the powder introduced from the feeder 6 is passed is formed. As shown in FIG. 3, a plurality of guide vanes 40 are disposed at equal intervals on the outer circumference of the centrifugal separation chamber 20, and the lower discotic member 24 is disposed below the centrifugal separation chamber 20. Along the outer circumferential wall of), a reclassification zone 28 is formed in which the powder dropped from the centrifugation chamber 20 after being centrifuged is blown back into the centrifugation chamber 20 again.

In the vicinity of the upper end of the outer circumferential wall of the reclassification zone 28, the ejection nozzle 30 for ejecting the high pressure gas supplied from the compressor 8 described above has the ejection direction substantially the same as the tangential direction of the outer circumferential wall. It is arranged. The jet nozzle 30 blows out the high pressure gas to disperse the powder injected from the inlet 26 and assists the gas into the centrifuge chamber 20. Further, the fine powder present in the reclassification zone 28 is blown back into the centrifuge chamber 20. On the other hand, in this embodiment, although the some jet nozzle 30 is arrange | positioned on the outer peripheral wall of the reclassification zone 28, this is an example and there exists freedom in the arrangement position and number of the jet nozzle 30. FIG.

In the center of the upper part of the centrifugal chamber 20, the suction port 32 which suction-recovers the coarse powder and the fine powder isolate | separated by centrifugation is provided. On the other hand, the coarse powder centrifugally separated from the reclassification zone 28 descends the inclined surface of the conical part of the classifier 4, and is discharged from the discharge port 34 provided at the bottom of the classifier 4, and the above-described recovery container ( 16) is accommodated in.

As shown in FIG. 3, in the outer peripheral part of the centrifugal chamber 20, the guide vane 40 which can form the turning airflow in this centrifugation chamber 20, and can adjust the turning speed of this turning airflow is arrange | positioned. It is. In addition, in this embodiment, 16 guide vanes 40 are arrange | positioned as an example. The guide vane 40 is pivotally rotatable between the upper disk-shaped member 22 and the lower disk-shaped member 24 by the rotation shaft 40a, and a pin ( 40b) engages with the rotating plate (rotating means) which is not shown in figure, and it is comprised so that all the guide vanes 40 may rotate at the same time simultaneously by rotating this rotating plate. In this way, the guide vane 40 is rotated by a predetermined angle to adjust the interval of each guide vane 40, thereby changing the flow velocity of the atmospheric gas passing through the gap in the direction of the white arrow shown in FIG. The flow velocity of the swirling airflow in the chamber 20 can be changed. By changing the flow velocity of the swirling airflow in this way, the classification performance (specifically, a classification point) of the classifier 4 which concerns on this embodiment can be changed. On the other hand, as described above, the atmospheric pressure gas passing through the interval of each guide vane 40 is the atmospheric pressure gas heated up to a predetermined temperature by the second heater 14 in advance.

Next, the classification method of powder which concerns on this embodiment is demonstrated using the flowchart of FIG. First, the powder to be classified and the liquid preparation are mixed (step S10). Next, the liquid preparation is vaporized by drying the mixture of powder and liquid preparation (step S12).

Examples of the powder to be classified include barium titanate, nickel and the like. As a liquid preparation, alcohol, such as ethanol and diethylene glycol monomethyl ether, is mentioned, for example. As a mixing ratio, it is 0.01 to 0.15 with respect to powder 1 normally at a mass ratio, Preferably 0.03 to 0.1 is added to powder 1, and it mixes. When this range is not satisfied, there arises a problem that the effect of the liquid preparation is not expressed or the fluidity of the powder is significantly reduced.

As a mixing method, the stirring using a stirrer and a magnetic stirrer, the planetary stirrer, the biaxial stirrer, the stirring using three rolls, etc. are mentioned. In this embodiment, a mixer ("Hi-X": manufactured by Nisshin Engineering Co., Ltd.) is used.

As a drying method, natural drying at room temperature, drying using a thermostat, etc. are mentioned. In addition, as dry conditions, it can select suitably according to the combination of powder and a liquid preparation, especially the flash point of a liquid preparation.

For example, when the powder is barium titanate and the liquid preparation is diethylene glycol monomethyl ether (flash point 93 ° C.), the drying temperature is usually 93 ° C. to 200 ° C., preferably using a constant temperature bath, from the viewpoint of working efficiency. Is 120 ° C to 200 ° C, and the drying time is usually 2 hours or less, preferably 30 minutes to 2 hours. When the liquid preparation is ethanol (flash point 16 ° C.), the drying temperature is usually 16 ° C. to 200 ° C., preferably 120 ° C. to 200 ° C., and the drying time is usually 2 using a thermostat in view of working efficiency. Time or less, Preferably it is 30 minutes-2 hours.

When the classification apparatus 2 is operated, suction of gas is started by the suction blower 12 (step S14). Since the gas in the centrifugal chamber 20 is sucked in from the suction port 32 provided in the upper center of the centrifugal chamber 20, the air pressure in the central portion of the centrifugal chamber 20 is relatively low. In this way, by the negative pressure generated in the centrifugal chamber 20, the atmosphere which is atmospheric pressure gas is sucked in between each guide vane 40 arrange | positioned along the outer periphery of the centrifugal chamber 20, and it enters into the centrifugal chamber 20. It is supplied (step S18). On the other hand, the atmospheric pressure gas sucked into the centrifugal chamber 20 is previously heated to a predetermined temperature by passing through the inside of the pipe provided in the second heater 14 (step S16). In this way, the atmospheric gas is sucked from between the guide vanes 40, so that a swirling airflow having a flow rate determined according to the rotation angle of the guide vanes 40 is formed. On the other hand, in the classification method of the powder according to this embodiment, the atmospheric pressure gas to be sucked is heated so that the temperature of the swirling air flow in the centrifugal separation chamber 20 becomes a desired temperature.

Next, the compressor 8 is used to start the supply of the high pressure gas toward the centrifuge chamber 20 of the classifier 4. The high pressure gas injected from the compressor 8 is heated to a predetermined temperature by the first heater 10 (step S20). On the other hand, like the 2nd heater 14, the 1st heater 10 heats the said high pressure gas so that the temperature of the turning airflow in the centrifugal chamber 20 may become desired temperature. The high pressure gas heated up to the predetermined temperature is blown out from the plurality of jet nozzles 30 provided on the outer circumferential wall of the centrifugal chamber 20 and supplied into the centrifugal chamber 20 (step S22).

As described above, when a state in which the heated high-speed swirling air flows normally in the centrifuge chamber 20 is formed, the mixed powder quantitatively discharged from the feeder 6 is transferred from the inlet 26 to the centrifugal chamber 20. It is thrown in (step S24). On the other hand, the mixed powder injected from the inlet 26 contains the liquid preparation which did not vaporize in the drying process shown by step S12 mentioned above.

As shown in FIG. 2, since the inlet 26 is provided above the outer peripheral portion of the centrifugal chamber 20, the mixed powder introduced from the inlet 26 allows the outer peripheral portion of the centrifugal chamber 20 at high speed. It collides with the turning air stream and disperses rapidly. At this time, the dispersion of the powder is promoted by rapidly vaporizing the liquid preparation mixed between the fine particles of the powder. In this way, the powder dispersed in the unit of fine particles does not adhere to the surfaces of the upper disk-shaped member 22, the lower disk-shaped member 24, etc. constituting the centrifugal chamber 20. It rotates several times and classifies according to the particle size of powder (step S26).

As a result of the centrifugal separation action in the centrifugal separation chamber 20, the fine powder having a particle size smaller than or equal to the desired classification point is concentrated in the central portion of the centrifugal separation chamber 20, and the upper discotic member 22 and the lower discotic member ( By the effect of the ring-shaped convex part provided in each center part of 24, it is collect | recovered from the suction port 32 with the gas sucked by the suction blower 12 (step S28). On the other hand, after the coarse powder having a particle size exceeding the classification point is concentrated on the outer peripheral part of the centrifugal chamber 20 by the centrifugal action in the centrifugal chamber 20, the classifier 4 is removed from the reclassification zone 28. ), The cone-shaped portion is dropped, discharged from the discharge port 34, and accommodated in the recovery container 16.

As described above, the powder dispersed effectively by the high temperature swing airflow and the liquid preparation effect that rotates inside the centrifugal separation chamber 20 is centrifuged without adhering to the surface of the components constituting the centrifugal separation chamber 20 and the like. The inside of the separation chamber 20 is swiveled and efficiently classified into fine powder below a desired classification point and remaining coarse powder. On the other hand, since the preparations supplied to the classifier 4 together with the powder are all vaporized, they are not included in the recovered powder.

In addition, in this embodiment, the gas supplied is heated so that the swirling airflow in the classifier 4 may become desired temperature, For example, the temperature of the swirling airflow in the classifier 4 is more than the flash point of the liquid preparation mixed with powder. Can be efficiently performed by heating the gas supplied so that it may become 200 degrees C or less.

Next, with reference to drawings, the classification method of powder which concerns on 2nd Embodiment of this invention is demonstrated. In addition, the structure of the classification method of the powder which concerns on this 2nd Embodiment removes the heating process of atmospheric pressure gas and high pressure gas in the classification method of powder which concerns on 1st Embodiment. Therefore, the detailed description of the same structure as the above-mentioned classification apparatus 2 is abbreviate | omitted, and only another part is demonstrated in detail. In addition, the same code | symbol is attached | subjected and demonstrated to the structure similar to the structure of the classification apparatus 2 mentioned above.

5 is a flowchart for explaining a method for classifying powder according to the second embodiment. First, the powder to be classified and the liquid preparation are mixed (step S30). Next, the liquid preparation is vaporized by drying the mixture of powder and liquid preparation (step S32). In addition, since the process shown to step S30 and S32 is the same as the process shown to step S10 and S12 of the flowchart of FIG. 4, detailed description is abbreviate | omitted.

When the classification apparatus 2 is operated, suction of gas is started by the suction blower 12 (step S34), and the atmosphere which is atmospheric pressure gas is supplied into the centrifugal separation chamber 20 (step S36). In this way, the atmospheric gas is sucked from between the guide vanes 40, so that a swirling airflow having a flow rate determined according to the rotation angle of the guide vanes 40 is formed. Next, the compressor 8 is used to start the supply of the high pressure gas into the centrifuge chamber 20 of the classifier 4 (step S38). Here, the high pressure gas is ejected from the plurality of jet nozzles 30 provided on the outer circumferential wall of the centrifugal chamber 20, and is supplied into the centrifugal chamber 20. In addition, in this embodiment, the normal pressure gas and the high pressure gas are not heated.

As described above, when a state in which the high-speed swinging air flows normally in the centrifugal chamber 20 is formed, the mixed powder quantitatively discharged from the feeder 6 is introduced into the centrifugal chamber 20 from the inlet 26. (Step S40). The mixed powder injected is classified according to the particle size of the powder (step S42), and recovered from the suction port 32 together with the gas sucked by the suction blower 12 (step S44). Moreover, the coarse powder which has a particle size exceeding a classification point is discharged | emitted from the discharge port 34 similarly to 1st Embodiment, and is accommodated in the collection container 16. As shown in FIG.

In addition, since the process shown to step S34, S36, S38, S40, S42, and S44 is the same as the process shown to step S14, S18, S22, S24, S26, and S28 of the flowchart of FIG. 4, detailed description is abbreviate | omitted. .

According to the classification method of the powder according to each of the embodiments described above, the powder to be classified is mixed with the liquid preparation, dried, and then charged into a centrifuge chamber in the classifier, and at a high speed by the gas sucked into the centrifuge chamber. Since the swirling airflow is formed, the powder and the liquid preparation are uniformly dispersed, so that the classification of the powder having a particle size of 1 µm or less can be efficiently performed.

Example

Next, the classification method of powder which concerns on this embodiment is demonstrated more concretely using an Example.

(Example 1)

As powder for classification, the fine powder of barium titanate (median diameter 0.683 micrometer, maximum particle diameter 7.778 micrometers) was used. Diethylene glycol monomethyl ether was used as a liquid preparation. In the mixing step, diethylene glycol monomethyl ether was added to the fine powder of barium titanate and mixed using a mixer ("Hi-X": manufactured by Nisshin Engineering Co., Ltd.). The addition amount of diethylene glycol monomethyl ether was 0.05 with respect to barium titanate 1 by mass ratio.

In a drying process, the mixture of barium titanate and diethylene glycol monomethyl ether was left to dry for 2 hours at 130 degreeC in a thermostat. The dried mixture was introduced into a classifier.

As a classifier, classification was performed using a classifier provided with a thermal insulation equipment, using 2 m ³ / min as the amount of gas to be sucked by the suction blower, and 0.6 MPa as the pressure of the high-pressure gas generated by the compressor. In addition, the injection amount of the powder to the classifier was set to 1 kg / hour, the atmospheric pressure gas and the high pressure gas were heated, and the temperature in the classifier was set to 100 degreeC. In addition, the temperature in a classifier was calculated | required by measuring the temperature of the gas immediately after inhaling from the suction port in a classifier by the suction blower of a classifier.

(Example 2)

The classification was performed under the same conditions as in Example 1 except that the temperature in the classifier was 18 ° C without heating the atmospheric pressure gas and the high pressure gas.

(Comparative Example 1)

The classification was performed under the same conditions as in Example 1 except that the drying in the drying step was not performed.

(Comparative Example 2)

The fine powder of barium titanate (median diameter 0.683 micrometer, maximum particle diameter 7.778 micrometer) was thrown into the classifier, without adding and mixing a liquid preparation. As conditions for classification in a classifier, it set as the conditions similar to Example 1 except having set the temperature in a classifier to 16 degreeC, without heating an atmospheric pressure gas and a high pressure gas.

(Assessment Methods)

The amount of barium titanate (based on dry powder) and the amount of product (fine powder) recovery in Examples and Comparative Examples were measured, and product yield was obtained. In addition, the product particle size (median diameter and maximum particle diameter) of the recovered fine powder was measured. In addition, the measurement of the particle diameter was performed using the particle diameter measuring apparatus ("Microtrack MT-3300EX": Nikki Corporation make). Table 1 shows the results of these measurements.

As shown in Table 1, when barium titanate and diethylene glycol monomethyl ether are mixed and dried, and heating is performed at the time of classification (Example 1), when drying before classification is not performed (comparative example) Compared with 1), it turned out that product recovery rate is more than equivalent.

In addition, when barium titanate and diethylene glycol monomethyl ether are mixed and dried, and heating is not performed at the time of classification (Example 2), when drying before classification is not carried out without adding liquid preparation (comparatively) It was found that the product recovery rate was higher than in Example 2).

Therefore, the product recovery rate of barium titanate was improved by drying.

On the other hand, in any of the examples 1 and 2 described above, centrifugation was continued for 30 minutes, but operation was not stopped due to the blockage. In addition, in any of the experimental results, it was confirmed that the particle size distribution of the recovered fine powder is equivalent, and even if the liquid preparation is added, it does not affect the classification performance itself at all.

2… Classifier, 4... Classifier, 6... Feeder, 8... Compressor, 10... First heater, 12... Suction blower, 14... Second heater, 20... Centrifuge chamber, 22... Upper discotic member, 24... Lower discotic member, 26... Inlet, 30... Jet nozzle, 32... Inlet, 40... Guide vanes.

Claims (8)

In the classification method of powder,
A mixing step of mixing the powder and the liquid preparation,
A drying step of drying the powder mixed in the mixing step,
An input step of injecting the powder dried in the drying step into a fluid classifier;
A heating step of heating the substrate,
A supply step of supplying the gas heated in the heating step to the fluid classifier;
And a classification step of classifying the powder in the fluid classifier according to the particle size. In the classification method of powder,
A mixing step of mixing the powder and the liquid preparation,
A drying step of drying the powder mixed in the mixing step,
An input step of injecting the powder dried in the drying step into a fluid classifier;
A supplying step of supplying gas to the fluid classifier;
And a classification step of classifying the powder in the fluid classifier according to the particle size. 3. The method according to claim 1 or 2,
The drying temperature and drying time in the said drying process are the drying temperature according to the flash point of the said liquid preparation, and drying time, The classification method of the powder characterized by the above-mentioned. The method of claim 1,
The said heating process heats the said gas so that the temperature in the said fluid classifier may be more than the flash point of the said liquid preparation, and 200 degrees C or less. 5. The method according to any one of claims 1 to 4,
The gas supplied in the feeding step is a high-pressure gas, characterized in that the classification method of powder. 6. The method according to any one of claims 1 to 5,
In the classification step, the powder is classified by the swirling air flow generated in the fluid classifier. 7. The method according to any one of claims 1 to 6,
Said liquid preparation is diethylene glycol monomethyl ether, The classification method of the powder characterized by the above-mentioned. The method according to any one of claims 1 to 7,
Said powder is a powder of barium titanate, The classification method of powder characterized by the above-mentioned.

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